Such decouplers are typically configured as belt pulley decouplers of a belt drive of an auxiliary unit of an internal combustion engine. These decouplers can be arranged as crankshaft decouplers on the crankshaft or as generator decouplers on the generator and compensate the input of torsional vibrations and cyclic irregularities of the crankshaft into the belt drive of the auxiliary unit or into the generator, as the case may be. In the engaged state of the one-way clutch, the series connection which is made up of the one-way clutch and the coil torsion spring transmits the drive torque from the drive part to the output part, and the elasticity of the coil torsion spring smooths the cyclic irregularities. When the rotation of the drive part is retarded, the one-way clutch is disengaged, so that, in reverse, no considerable torque can be transmitted from the output part to the drive part. In the case of the generator decoupler, the generator shaft, which possesses a relatively high mass inertia, can overrun the belt pulley of the generator.
A generic type of generator decoupler is disclosed for example in U.S. Pat. No. 8,047,920 B2. A one-way clutch is configured as a wrap-around band which is situated in the series connection on the drive side and radially between the coil torsion spring and the belt pulley. Although the wrap-around band is disengaged when the generator shaft is in the overrunning state, the frictional torque between the inner peripheral surface of the belt pulley and the wrap-around band clinging thereto can lead to a relative twisting of the two spring collars, so that the ends of the coil torsion springs move away from the peripheral contact sections of the ramp-like spring collars and move upwards along their ramps. Because, due to the ramp geometry, the available axial design space for the coil torsion spring gets effectively reduced during this upward motion, it is possible for the coil torsion spring to press the two spring collars axially apart from each other and thus cause, as it were, a bursting of the belt pulley coupler in the axial direction. An equally undesired consequence is the conspicuous noise generated by the decoupler when one or both of the spring ends run repeatedly upwards along the ramps and snap back against the stops after each revolution.
As a solution to this problem U.S. Pat. No. 8,047,920 B2 proposes a mechanism that blocks the undesired relative twisting of the two spring collars. According to this solution, during overrunning operation, the two spring collars rotate synchronously and as a unit with the coil torsion spring to thus prevent the upward movement of the spring ends along the ramps. The blocking action is realized through a construction having rotary stops which are fixed on the one hand to the output part and on the other hand on the drive-side spring collar and entrain this spring collar during overrunning operation.